mir-17~92 Deletion in Alveolar Type 2 Epithelial Cells vs Alveolar Fibroblasts Have Disparate Effects on Neonatal Alveolar Development

Mary E. Robbins, Ann & Robert H. Lurie Children's Hospital of Chicago, Chicago, IL, United States; Joann M. Taylor, Stanley Manne Research Institute at Ann and Robert H Lurie Children's Hospital of Chicago, United States; Nikolay Markov, Northwestern University, United States; Ziyan Lu, Northwester University, United States; Alexander Misharin, Northwestern University, Division of Pulmonary and Critical Care Medicine, United States; GR Scott Budinger, Northwestern University, Division of Pulmonary and Critical Care Medicine, United States

Background: Bronchopulmonary dysplasia (BPD) causes significant morbidity and mortality in premature infants. Although mechanisms causing the abnormal lung structure found in BPD are poorly understood, prior work has shown that effecting either part of the Alveolar Type 2 (AT2) Epithelial Cell and Alveolar Fibroblast (AF) stem-cell niche produces alveolar simplification reminiscent of BPD. We have previously reported that microRNA (miR)-17~92 expression is severely attenuated in human patients who died from BPD and confirmed this in a murine disease model. Global deletion of miR-17-92 results in fatal neonatal respiratory failure from alveolar epithelial hypoplasia; however, the cell specific effects of miR-17-92 deletion on alveolar development are not known.

Objectives: We hypothesize that miR-17~92 deletion in AT2 or AF will cause alveolar simplification reminiscent of a BPD-like phenotype.

Design/Methods: We used an inducible, fluorescent, lox-cre system (miR-17~92flox/flox x ER-SPCCre x zsGreen and miR-17~92flox/flox x ER-PDGFR-aCre x zsGreen) combined with flow cytometry, microscopy and bulk RNA-seq to characterize the impact of miR-17-92 in AT2 vs AF during postnatal alveologenesis. Tamoxifen administration on the day of birth allow for targeting cells prior to alveologenesis beginning on day 4.

Results: Using a tamoxifen-inducible fate-mapping system, we achieved >98% of miR-17-92 deletion. With AT2-specific deletion, we demonstrated deficiencies in structural lung development evidenced by increased alveolar area that was not seen in AF-specific deletion. AT2-specific deletion caused upregulation in cell death and downregulation of lipid metabolism gene ontogeny processes.

Conclusion: Our data supported the hypothesis that miR-17~92 deletion in AT2 cells produces alveolar simplification classically found in oxygen-induced BPD models. Likely related to metabolic failure and cell death, the AT2 cells’ ability to transdifferentiate into the alveolar type 1 epithelial cells, which comprise the alveoli walls, may have been compromised. However, the same effect on structural lung development was not found when the AF within the stem-cell niche was targeted. Pending transcriptomic data in AF-deletion will provide insight regarding developmental pathways differentially influenced by miR-17-92 based on cell type. This inducible, cell-specific model provides a unique opportunity to elucidate the biologic impact of miR-17~92 on alveolar development.